Out of ideas

351wstangjk said:

One question I have is it possible to fry part of the ECU but not the whole thing? I have tried everything I can think of, please any input would be appreciated

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I've fixed a Mustang that had idle problems, as if the IAB was stuck open... The guy sent the car to two garages, changed most of the sensors... The car started up great but would revv past 3000rpm at idle unless you unplugged the IAB.

I took apart the EFI harness and found a short in the IAB wires, fixed the harness but the car still worked like junk. I changed the computer and now his car runs like a dream.

You have a lot of codes, try to cure those before changing the computer. Or put that computer in another Mustang and see if the problems persists.

Codes: 41 & 91
What ecu are you using?
What injectors are you using?
What MAF meter/sensor are you using?

Code 29:
Did you install the VSS?

Code 61:
Check the ECT output at the ecu.

That is all I can think of off the top of my head...

JRichker has some excellent writeups on tracking/fixing diagnostic codes...

jason

Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.



The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.


You mentioned a C&L MAF: do you have the MAF sensor that matches the computer? Have you tried rotating the MAF housing to see if it changes the operation of the engine?

Glad you got it nailed down! Thanks for the update.